Cancer cells characteristically exhibit an abnormal regulation of genetic activity. A useful model for studying dramatic changes in gene activity is the chick-HeLa system. Terminally differentiated 14-day old chick embryo erythrocytes can be fused with HeLa cells in the presence of U-V inactivated Sendai virus. In the HeLa cytoplasm the erythrocyte nucleus acquires HeLa protein and subsequently resumes DNA and RNA synthesis. DNA doubles within 48 hours post-fusion (work of others). I propose to: 1) separate the nuclear nonhistone proteins of erythrocyte and HeLa cells into three classes based on solubility; 2) characterize each class by electrophoretic separation of the component subunit proteins according to molecular weight; 3) prepare antibodies in rabbits against the solubility classes; 4) determine cross reactivity between the HeLa and chick proteins; 5) isolate the reactivated erythrocyte nuclei from the heterokaryons 24 and 48 hours post-fusion and prepare the three solubility classes of protein; 6) characterize the proteins of the reactivated nucleus by electrophoretic migration and specific immunoprecipitation; 7) assess the intranuclear location of the classes of protein by indirect immunofluorescence assay. These experiments are designed to characterize a group of proteins capable of restoring functionality to a genetically inactive nucleus.